Dynamic Average if formula

Hi all,

I need a formula to calculate an average score (Col I) of a person (Col F) but the average range will move around so it needs to be dynamic (i.e. use column that contains "M2")

Example worksheet attached.

The formula should be entered into B2,3,4.

I am using excel at the moment but this will be used in Google sheets so ideally I need the formula to work in google sheets.

Thanks in advance
Dc